Global warming poses a particular threat of rapid disintegration to the southern part of the Greenland ice sheet, according to new research.

Ice sheet flow is accelerated by sudden pulses of water due to cycles of day-time melting and rainfall whereas higher rates of steady water flow linked with continuous melting “can suppress, rather than enhance” the thinning of ice sheets, researcher Christian Schoof writes in a new paper. This is significant as the rate of ice sheet disintegration is a key uncertainty in estimates of the potential for sea level rises.

Since the southern part of the Greenland ice sheet is at lower latitudes compared with both northern Greenland and Antarctica it experiences a more pronounced diurnal cycle of day-time melting which leads to significant daily pulses of melt water in the summer. While more frequent rain events linked to climate change would also have an impact on the south of Greenland, according to Schoof who works at the University of British Columbia in Canada.

Schoof writes that “diurnal melt cycles already contribute to ice flow in southern Greenland, and more frequent rain events are predicted to result from a northward shift of storm tracks over the next century, which will cause further ice acceleration”. His paper “Ice-sheet acceleration driven by melt supply variability” is published in the 9 December edition of Nature.

Glaciologist Martin Luthi of the ETH science university in Zurich describes Schoof's work as a “milestone study” of subglacial drainage because for the first time it shows how the drainage systems of ice sheets switch between different modes and adapt to variations in the flow of water from the surface, and why it is these variations in water flow, rather than the total water volume that drives the acceleration of ice sheets.

Schoof makes it clear in his paper that it is spikes in water flow along the base of the ice sheet that lead to ice flow acceleration and that these are driven by strong diurnal melt cycles and an increase in rain and surface lake drainage events rather than an increase in mean melt supply.

Increased ice velocities in Greenland are contributing significantly to a sea level rise and recent observations of a link between surface melt and ice acceleration have raised the possibility of a positive feedback in which surface melting and accelerated dynamic thinning reinforce one another, suggesting that overall warming could lead to accelerated mass loss. Schoof's paper suggests that the process is more complicated than this.